Why should they? Are these people going to abandon their Macs because of these bugs? Obviously not, so why should Apple spend any money at all fixing them?
It's a winning business strategy, especially when you have legions of die-hard customers who won't leave you. Microsoft has a similar situation (though many probably won't leave MS for different reasons), so it's in their business interest to increase profits by subjugating their customers with annoying ads baked into the OS. What do they have to lose? It's not like Apple's/MS's customers are going to switch to Linux (which has its own problems of course).
To be fair to Apple, it does sound like this is a somewhat rare bug (only seen in high-load situations?). It's not as bad, I think, as ads in the OS. So, as you say, Apple just needs to be a little better than MS and that's good enough.
Except apple does also put ads in their os. And you can't even permanently disable them, the iCloud nagware comes back every once in a while trying to sell me overpriced storage.
While it is annoying, I've got much better audio performance and less hassle from macOS than with Linux or Windows, even with bugs.
There were a few audio bugs that annoyed me in the '2020 videoconferencing season', but most were solved. I've noticed the L/R volume bug then, but not in the last few years and my perception was it was fixed. So, even if it's buggy it might not be buggy for everyone.